Method and apparatus for trimming aluminum sheet

ABSTRACT

A method and apparatus are provided for reducing or eliminating sliver formation during aluminum sheet trimming operations. By controlling parameters such as trimming angle and cutting blade clearance, aluminum sheet can be trimmed while substantially eliminating the formation of slivers which damage the surface finish of the part. Cutting angle and clearance are preferably selected such that a wide range of cutting blade sharpnesses produce satisfactory cuts. The method and apparatus are particularly useful for trimming aluminum autobody sheet.

FIELD OF THE INVENTION

[0001] The present invention relates to trimming or shearing of aluminum sheet, and more particularly relates to a method and apparatus for reducing sliver production during trimming of sheet such as aluminum autobody sheet.

BACKGROUND INFORMATION

[0002] Automotive manufacturers are seeking ways of replacing steel components with aluminum components in order to gain benefits such as reduced weight and improved corrosion resistance. For example, attempts have been made to replace conventional steel autobody sheet with aluminum autobody sheet.

[0003] Trimming is an important operation in the autobody sheet forming process. Such trimming operations have conventionally been used to form steel sheet having adequate edge characteristics. When trimmed with dies conventionally designed for steel sheet, aluminum autobody sheet produces unacceptable cut surfaces having slivers, burrs, surface roughness and the like. Slivers are particularly disadvantageous because they cause damage to both the tooling and surface finish of the part. In addition, slivers contaminate the production line.

[0004] Sliver production has been recognized by automotive manufacturers as a critical problem in the utilization of aluminum in the automotive industry. Currently, there is no effective procedure for eliminating sliver production during the formation of aluminum autobody sheet. Instead, hand finishing of the formed aluminum parts and hand removal of the slivers are usually employed in production practice. The present invention has been developed in view of the foregoing and to remedy other deficiencies of the prior art.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to control the slivering of aluminum sheet during trimming processes.

[0006] Another object of the present invention is to reduce the frequency of tool sharpening required during aluminum sheet trimming operations.

[0007] A further object of the present invention is to provide an aluminum sheet trimming operation in which the cutting blade clearance can be varied over a relatively wide range.

[0008] Another object of the present invention is to provide a method of trimming aluminum including the steps of cutting the aluminum sheet at a cutting angle and with a cutting blade clearance which substantially eliminate the formation of aluminum slivers.

[0009] A further object of the present invention is to provide a method of trimming aluminum sheet including the steps of securing an aluminum sheet at a cutting angle of at least about 10 degrees adjacent a cutting blade, trimming the aluminum sheet at the cutting angle with the cutting blade, and recovering the trimmed aluminum sheet with substantially no slivers.

[0010] Another object of the present invention is to provide a method of trimming aluminum sheet including the steps of securing the aluminum sheet between a die and a pad, trimming the aluminum sheet at a cutting blade clearance of greater than about 15% of the thickness of the aluminum sheet, and recovering the trimmed aluminum sheet with substantially no slivers.

[0011] A further object of the present invention is to provide an apparatus for reducing sliver production during trimming of aluminum sheet including means for cutting the aluminum sheet, and means for securing the aluminum sheet adjacent the cutting means at a cutting angle of at least about 10 degrees.

[0012] Another object of the present invention is to provide a trimmed aluminum sheet substantially free of slivers produced by securing an aluminum sheet at a cutting angle of at least about 10 degrees adjacent a cutting blade, and trimming the aluminum sheet at the cutting angle with the cutting blade.

[0013] These and other objects of the present invention will become more apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a partially schematic illustration of a conventional apparatus for trimming steel autobody sheet.

[0015]FIG. 2 is a partially schematic illustration of an aluminum sheet trimming apparatus in accordance with an embodiment of the present invention.

[0016]FIG. 3 is a partially schematic illustration of an aluminum sheet trimming apparatus of the present invention, showing the parameters of cutting angle, clearance and tool sharpness.

[0017]FIG. 4 is a partially schematic illustration of an aluminum sheet being trimmed in accordance with an embodiment of the present invention.

[0018]FIG. 5 is a photomicrograph of conventional AKDQ steel autobody sheet at a magnification of 250×.

[0019]FIG. 6 is a photomicrograph of conventional DQIF steel autobody sheet at a magnification of 250×.

[0020]FIG. 7 is a photomicrograph of Aluminum Association 6111-T4 aluminum alloy sheet which may be trimmed in accordance with the present invention, at a magnification of 250×.

[0021]FIG. 8 is a photomicrograph of Aluminum Association 6022-T4 aluminum alloy sheet which may be trimmed in accordance with the present invention, at a magnification of 250×.

[0022]FIG. 9 is a graph showing the effects of cutting angle in trimming steel and aluminum sheet.

[0023]FIG. 10 is a graph showing the effects of cutting blade clearance in trimming steel and aluminum sheet.

[0024]FIG. 11 is a graph showing the effects of tool sharpness in trimming steel and aluminum sheet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025]FIG. 1 schematically illustrates a conventional apparatus for cutting sheet metal such as steel autobody sheet. A metal sheet 10 is sandwiched between a die 12 and a pad 14. A cutting blade 16 travels in the direction 17 adjacent the die 12 and pad 14 to trim the sheet 10. In this apparatus, the strain field 18 comprises a shear strain τ with essentially no normal stress. It is known that for steel sheet, a zero degree cutting angle as shown in FIG. 1 produces the most desirable cut edge and generates the least amount of slivers. Conventional trimming apparatus designs therefore minimize any deviation of the cutting angle from zero degrees. Furthermore, when trimming steel sheet, it is critical to maintain sharp tools and keep clearances below about 8 percent of the metal sheet thickness in order to obtain satisfactory cut edges. However, when such conventional steel sheet trimming methods are applied to aluminum sheet, the use of a zero degree cutting angle has been found to produce an unacceptably high amount of slivers for both 6111-T4 and 6022-T4 aluminum alloy sheets.

[0026]FIG. 2 schematically illustrates an apparatus for trimming aluminum sheet in accordance with the present invention. An aluminum sheet 20 is secured between a die 22 and a pad 24. A cutting blade 26 travels in the direction 27 adjacent the die 22 and pad 24 to trim the aluminum sheet 20. The configuration shown in FIG. 2 produces a strain field 28 having a shear strain component τ and a normal stress component σ. In accordance with the present invention, the normal stress component σ is used to improve the cut edge of the aluminum sheet 20 by enhancing ductile fracture.

[0027] As shown most clearly in FIG. 3, the aluminum sheet 20 has a thickness T. The sheet thickness T preferably ranges from about 0.5 to about 1.5 mm, more preferably from about 0.7 to about 1.1. mm. For aluminum autobody sheet, the thickness is typically about 1 mm. The aluminum sheet 20 is positioned with a cutting angle A through use of the die 22 and the pad 24 having opposing angled surfaces which contact the surfaces of the aluminum sheet 20. The cutting blade 26 is positioned with a clearance C from the die 22 and pad 24. In accordance with a preferred embodiment, the clearance C is at least about 10 percent of the thickness T of the aluminum sheet 20. In contrast, the clearance used for trimming steel sheet is conventionally kept below about 8 percent of the steel sheet thickness in order to obtain satisfactory cut edges.

[0028] As shown in FIG. 3, the cutting blade 26 comprises an edge having a tool sharpness R defined as the blade edge radius. During repeated trimming processes, the cutting blade 26 loses sharpness and becomes increasingly dull with values of R ranging from about 0.002 to about 0.75 mm and higher. In accordance with the present invention, the trimming angle A and clearance C are preferably controlled in order to tolerate a tool sharpness R of at least 0.1 mm (0.004 in.), more preferably at least 0.125 mm (0.005 in.), and most preferably at least 0.25 mm (0.01 in.).

[0029] The cutting angle primarily determines the shear stress and normal stress components on the cutting surface of the sheet. A zero degree cut results in the least amount of normal stress. The normal stress component increases as the cutting angle increases. The cutting angle A shown in FIG. 3 used in accordance with the present invention produces a tensile normal stress component which helps the ductile fracture of the aluminum alloy sheet. The cutting angle A used in the trimming operation of the present invention promotes ductile fracture which involves void nucleation, growth and coalescence, as well as the formation and propagation of a localization zone. However, as the cutting angle A increases significantly, the normal stress component becomes so large that the trimming operation can be adversely effected. As discussed more fully below, depending on the particular cutting blade clearance used, the cutting angle A may preferably be greater than about 10 degrees, and more preferably may range from about 10 to about 25 degrees. Such relatively large cutting angles have been found to substantially reduce or eliminate the formation of slivers during the aluminum trimming operation and to permit the satisfactory use of cutting blades for a relatively long time before sharpening is required.

[0030] As shown in FIG. 3, the clearance C effects the shear strain level in the deformation zone such that the average shear strain in the deformation zone is equal to the blade travel displacement divided by the clearance. Thus, for the same blade travel displacement, a smaller clearance produces a higher shear strain. In conventional trimming of steel sheet, a small clearance is critical because steel has very high ductility. In contrast, the clearance C used in trimming aluminum alloy sheet can be varied within a relatively wide range. The clearance C is typically greater than about 10 percent of the thickness of the aluminum sheet, preferably from about 10 to about 15 or 20 percent of the thickness of the aluminum sheet.

[0031]FIG. 4 illustrates an aluminum sheet 20 being trimmed. About 80 percent of slivers occur at the blade contact zone 31, with minor amounts of slivers occurring at the burr area 32 or fracture surface 33.

[0032] In trimming operations, a sharp blade results in more concentrated deformation than a dull blade. The highly concentrated stresses produced by a sharp blade result in highly concentrated strain or strain localization. It has been conventionally recognized that sharper tools perform better in the trimming process than dull tools. However, in accordance with the present invention, the cutting angle A and the clearance C used in trimming aluminum alloy sheet are preferably controlled in a manner that allows relatively dull blades to shear the aluminum sheet satisfactorily.

[0033] In accordance with the present invention, the cutting condition for aluminum alloys such as 6111-T4 differs substantially from the cutting condition for conventional steel sheet. As shown in FIGS. 4-7, steel and aluminum alloys have fundamentally different microstructures. The AKDQ steel sheet shown in FIG. 5 and the DQIF steel sheet shown in FIG. 6 have a clean microstructure having very few if any precipitates, dispersoids and constituents. In contrast, the 6111-T4 aluminum sheet shown in FIG. 7 and the 6022-T4 aluminum alloy sheet shown in FIG. 8 contain substantially more precipitates, dispersoids and constituents. These second phase particles make the fracture of aluminum alloys much more sensitive to tensile stresses than steel, which has significantly higher ductility than aluminum alloys. Other microstructural differences between steel and aluminum such as body centered cubic (BCC) and face centered cubic (FCC) crystal structures play important roles in the ductility of the alloys. While trimming of aluminum alloys 6111 and 6022 is primarily disclosed herein, it is to be understood that other alloys may be trimmed in accordance with the present invention. Such additional alloys typically contain similar types and/or amounts of precipitates or dispersoids, and undergo ductile fracture in a manner similar to 6111 and 6022 alloys.

EXAMPLES

[0034] The trimming variables evaluated include cutting angle, clearance and blade sharpness. The laboratory tooling used to trim each sheet is capable of cutting sheet with 0°, 5°, 10°, 15°, 20° and 25° trimming angles. The clearances evaluated were 5%, 10%, 15%, 20% and 25% of the sheet thickness for 6111-T4 and 6022-T4 sheets with a nominal thickness of 0.040 in. (1 mm). Six blade sharpnesses were evaluated. The blade sharpness is quantified by the cutting edge radius. The sharpest one had a cutting edge radius of 0.0001-0.0004 in. (2-10 μm). Other blade sharpnesses evaluated were 0.001 in. (25 μm), 0.002 in. (50 μm), 0.005 in. (125 μm), 0.010 in. (0.25 mm), and 0.020 in. (0.5 mm). The reason for the sharpest blades not having a definite cutting edge radius is that their edge radii were too small to be exactly quantified on the available measuring device. In addition, such sharp blades would wear after only a few cuts and their sharpnesses would vary.

[0035] A total of 130 cutting conditions were evaluated. These conditions included different combinations of cutting angles, clearances and blade sharpnesses. The dimensions of the sheet test samples were 1.5 in.×5.0 in. All samples were tested under unlubricated conditions using straight blades/pads. Within each cutting condition, the effects of sheet orientation were evaluated with samples prepared parallel to and transverse to the rolling direction. About 1,500 samples for each of the two aluminum alloys were tested. For comparison, selected cutting conditions were evaluated for 0.031 in. (0.79 mm) AKDQ steel automotive sheet and 0.029 in. (0.74 mm) DQIF steel automotive sheet.

[0036] The observations were focused on the sliver generation. However, the severity of burr formation and the quality of the cut surface are also of concern. The severity of the burr is quantified by the burr height. The quality of the cut surface is represented by its roughness.

[0037] Table 1 and Table 2 summarize the results of 6111-T4 and 6022-T4 cut with the sharpest blades which had edge radii R of 0.0001-0.0004 in. (2-10 μm). The cut surface quality is generally acceptable for all cutting conditions with such blade sharpnesses.

[0038] As the clearance or cutting angle increases, the burnish area and the secondary-burnish area decrease while the fracture area increases. Hairlike slivers generated by the cuts along the longitudinal (rolling) direction appear longer than those generated by the cuts perpendicular to the longitudinal (rolling) direction. There is no distinguishable difference in burr height and cut surface quality between the cuts along or perpendicular to the longitudinal (rolling) direction.

[0039] Table 3 and Table 4 present the results for 6111-T4 and 6022-T4 cut with the blades of cutting edge radii R of 0.001 in. (25 μm) and 0.002 in. (50 μm), respectively. These two blade sharpnesses produce very similar results. The 0.002 in. blade generates slightly bigger (wider) pieces of hairlike slivers and slightly higher burrs than the 0.001 in. blade. The cut surface quality is generally acceptable for all cutting conditions with these two blade sharpnesses. As the clearance C or cutting angle A increases, the burnish area and the secondary burnish area decrease while the fracture area increases. The secondary burnish area eventually disappears as clearance and cutting angle increase. Hairlike slivers generated by the cuts along the longitudinal (rolling) direction appear longer than those generated by the cuts perpendicular to the longitudinal (rolling) direction.

[0040] The appearance of slivers changes when the blade edge radius reaches 0.005 in. (125 μm). The amount of hairlike slivers is drastically reduced. However, they are replaced by slivers of large metal pieces and small particles. The cut surface quality declines compared to the cuts by blades with sharpnesses of 0.0001-0.0002 in., 0.001 in. and 0.002 in. Table 5 summarizes the results for 6111-T4 and 6022-T4 for the blades of 0.005 in. With this blade sharpness and small cutting angles (0-10 degrees) and for large clearances (15-25%), the roughness of the cut surface increases significantly as the clearance increases.

[0041] Table 6 and Table 7 show the results of 6111-T4 and 6022-T4 trimmed by blades with cutting edge radii of 0.010 in. (0.25 mm) and 0.020 in. (0.50 mm). These blades are considered very dull for cutting sheets of 0.040 in. (1 mm) thick. With these blades, although almost no hairlike slivers are generated, the slivers are in the form of either large metal pieces or small particles. However, with 15-25 degree cutting angles and 5-10% clearances, no slivers in any form are generated and the burr is minimal for blades with edge radii up to 0.020 in. The quality of the cut surface is also very good.

[0042] It is observed that the majority of slivers occur during the down stroke. The press used for the testing is a two-step press. It can be interrupted after the down stroke and then resumed for the back stroke. The conclusion that the majority of slivers occur during the down stroke is also reached from intensive micrographic investigations to trace the origin of slivers.

[0043] About 150 steel samples were cut under selected combinations of cutting angle, clearance and blade sharpness. The restrictions placed on trimming angle, clearance and blade sharpness for cutting steel sheets are due to concerns about being able to cut off the metal with acceptable burr heights and good cut surfaces. Table 8 shows the representative maximum clearance and blade sharpnesses for cutting DQIF steel sheet. TABLE 1 6111-T4 (BLADE SHARPNESS = 0.0001-0.0004 In.) 0 Degree 5 Degree 10 Degree 15 Degree 20 Degree 25 Degree  5% Clearance Significant amount fine Some fine hairlike Almost no slivers; very No slivers; minimal burr No slivers; minimal burr No slivers; minimal burr hairlike slivers; slight slivers; slight burr on slight burr on edge on edge on edge on edge burr on edge edge 10% Clearance Some fine hairlike Some slivers; slight burr No slivers; slight burr on No slivers; minimal burr No slivers; minimal burr No slivers; minimal burr slivers; slight burr on on edge edge on edge on edge on edge edge 15% Clearance Almost no slivers; slight Almost no slivers; slight No slivers; slight burr on No slivers, very slight No slivers; minimal burr No slivers; minimal burr to medium burr on edge to medium burr on edge edge burr on edge on edge on edge 20% Clearance No slivers; medium burr No slivers; medium burr No slivers; very slight No slivers; very slight No slivers; very slight No slivers; minimal burr on edge on edge medium burr on edge burr on edge burr on edge on edge 25% Clearance No slivers; medium burr No slivers; medium burr No slivers; slight to No slivers; slight burr on No slivers; very slight No slivers; very slight on edge on edge medium burr on edge edge burr on edge burr on edge

[0044] TABLE 2 6022-T4 (BLADE SHARPNESS = 0.0001-0.0004 In.) 0 Degree 5 Degree 10 Degree 15 Degree 20 Degree 25 Degree  5% Clearance Significant amount fine Many fine hairlike Little to no slivers; very Almost no slivers; No slivers; minimal burr No slivers; minimal burr hairlike slivers; slight slivers; very slight slight burr on edge minimal burr on edge on edge on edge burr on edge burr on edge 10% Clearance Many fine hairlike Many slivers; very slight Almost no slivers; slight No slivers; minimal burr No slivers; minimal burr No slivers; minimal burr slivers; slight burr on burr on edge burr on edge on edge on edge on edge edge 15% Clearance A few slivers; slight A few slivers; slight No slivers; slight burr on No slivers, very slight No slivers; minimal burr No slivers; minimal burr to medium burr on edge to medium burr on edge edge burr on edge on edge on edge 20% Clearance Almost no slivers; No slivers; medium burr No slivers; slight No slivers; very slight No slivers; very slight No slivers; minimal burr medium burr on edge on edge to medium burr on edge burr on edge burr on edge on edge 25% Clearance No slivers; medium burr No slivers; medium burr No slivers; slight to No slivers; slight burr on No slivers; very slight No slivers; very slight on edge on edge medium burr on edge edge burr on edge burr on edge

[0045] TABLE 3 0 Degree 10 Degree 20 Degree 25 Degree 6111-T4 (BLADE SHARPNESS = 0.001 in.)  5% Clearance Significant amount of long Some hairlike slivers; very No slivers; minimal burr No slivers; minimal burr hairlike slivers; slight burr slight burr 10% Clearance Many hairlike slivers; slight to A few slivers; slight burr No slivers; minimal burr No slivers; minimal burr medium burr 15% Clearance Some slivers; slight to medium No slivers; slight burr No slivers; slight burr No slivers; very slight burr burr 20% Clearance No slivers; medium burr No slivers; slight to medium No slivers; slight burr No slivers; slight burr burr 25% Clearance No slivers; medium burr No slivers; medium burr No slivers; medium burr No slivers; slight burr 6022-T4 (BLADE SHARPNESS = 0.001 in.)  5% Clearance Significant amount of long Many hairlike slivers; very No slivers; minimal burr No slivers; minimal burr hairlike slivers; slight burr slight burr 10% Clearance Many hairlike slivers; slight to Some slivers; slight burr No slivers; minimal burr No slivers; minimal burr medium burr 15% Clearance Some slivers; slight No slivers; slight burr No slivers; slight burr No slivers; very slight burr to medium burr 20% Clearance No slivers: medium burr No slivers; slight to medium No slivers; slight burr No slivers; slight burr burr 25% Clearance No slivers: medium burr No slivers; medium burr No slivers; medium burr No slivers: slight burr

[0046] TABLE 4 0 Degree 10 Degree 20 Degree 25 Degree 6111-T4 (BLADE SHARPNESS = 0.002 in.)  5% Clearance Significant amount of hairlike Many hairlike slivers; very No slivers; minimal burr No slivers; minimal burr slivers slight to medium burr slight burr 10% Clearance Many hairlike slivers; slight to A few slivers; slight burr No slivers; minimal burr No slivers; minimal burr medium burr 15% Clearance Some slivers; medium burr No slivers; slight to medium No slivers; slight burr No slivers; very slight burr burr 20% Clearance No slivers; medium burr No slivers; slight to medium No slivers; slight No slivers; slight burr burr to medium burr 25% Clearance No slivers; medium burr No slivers; medium burr No slivers; medium burr No slivers; slight to medium burr 6022-T4 (BLADE SHARPNESS = 0.002 in.)  5% Clearance Significant amount of hairlike Some hairlike slivers; very No slivers; minimal burr No slivers; minimal burr slivers; slight to medium burr slight burr 10% Clearance Many hairlike slivers; slight to Some slivers; slight burr No slivers; minimal burr No slivers; minimal burr medium burr 15% Clearance Some slivers; medium burr No slivers; slight to medium No slivers; slight burr No slivers; very slight burr burr 20% Clearance No slivers; medium burr No slivers; slight to medium No slivers; slight to medium No slivers; slight burr burr burr 25% Clearance No siivers; medium burr No slivers; medium burr No slivers; medium burr No slivers; slight to medium burr

[0047] TABLE 5 0 Degree 10 Degree 20 Degree 25 Degree 6111-T4 (BLADE SHARPNESS = 0.005 in.)  5% Clearance A few hairlike sliver Almost no hairlike No slivers; minimal burr, No slivers; minimal burr, and some large slivers, some large good cutting surface good cutting surface peice slivers and particles pieces slivers and particles; medium burr, fair cutting slight burr, fair cutting surface surface 10% Clearance Almost no hairlike slivers, Almost no hairlike slivers; No slivers, minimal burr, No slivers; minimal burr, some large pieces a few large piece slivers; fair cutting surface fair cutting surface slivers and particles; medium medium to high burr burr, fair cutting surface rought cutting surface 15% Clearance Almost no hairlike slivers; No sliver; medium to high burr No slivers; medium burr, No slivers; slight to medium burr, a few large piece slivers; rough cutting surface rough cutting surface rough cutting surface medium to high burr fair cutting surface 20% Clearance No slivers; medium to high No slivers; high burr, very No slivers; medium to high burr, No slivers; medium burr, burr, rough cutting surface rouhg cutting surface very rough cutting surface very rough cutting surface 25% Clearance No slivers, high burr, No slivers, high burr, No slivers, high burr No slivers; medium to high burr rough cutting surface very rough cutting surface very rough cutting surface rough cutting surface 6022-T4 (BLADE SHARPNESS = 0.005 in.)  5% Clearance A few hairlike sliver Almost no hairlike No slivers; minimal burr, No slivers; minimal burr, and some large slivers, some large good cutting surface good cutting surface peice slivers and particles pieces slivers and particles; medium burr, fair slight burr, fair cutting surface cutting surface 10% Clearance Almost no hairlike slivers, Almost no hairlike slivers; No slivers, minimal burr, No slivers; minimal burr, some large pieces a few large piece slivers; fair cutting surface fair cutting surface slivers and particles; medium medium to high burr burr, fair cutting surface rought cutting surface 15% Clearance Almost no hairlike slivers; No sliver; medium to high burr No slivers; medium burr, No slivers; slight to medium burr, a few large piece slivers; rough cutting surface rough cutting surface rough cutting surface medium to high burr fair cutting surface 20% Clearance No slivers; medium to high No slivers; high burr, very No slivers; medium to high burr, No slivers; medium burr, burr, rough cutting surface rouhg cutting surface very rough cutting surface very rough cutting surface 25% Clearance No slivers, high burr, No slivers, high burr, No slivers, high burr No slivers; medium to high burr rough cutting surface very rough cutting surface very rough cutting surface rough cutting surface

[0048] TABLE 6 0 Degree 10 Degree 20 Degree 25 Degree 6111-T4 (BLADE SHARPNESS = 0.010 in.)  5% Clearance Almost no hairlike sliver almost no hairlike slivers, No slivers, minimal burr, No slivers, minimal burr, and may large piece slivers some large pieces slivers and good cutting surface good cutting surface and particles, high burr, minimal burr, fail cutting surface rough cutting surface 10% Clearance No hairlike slivers, some No hairlike slivers, a few No slivers, minimal burr, No slivers, minimal burr, large pieces slivers and large piece slivers; high burr good cutting surface good cutting surface and particles; very high unacceptably rough cutting burr, rough cutting surface surface 15% Clearance No hairlike slivers, a few No slivers, high burr, No slivers, high burr, No slivers, high burr large piece slivers; very high unacceptably rough cutting surface rough cutting surface rough cutting surface high burr, rough cutting surface 20% Clearance No slivers, extremely high burr, No slivers, very high burr, No slivers, high burr, No slivers; high burr, very rough cutting surface unacceptable rough cutting unacceptably rough cutting unacceptable rough cutting surface surface surface 25% Clearance No slivers, extremely high burr, No slivers; extremely high No slivers; extremely high No slivers, very high burr, very rough cutting surface burr, unacceptably rough burr, unacceptably unaccetably rough cutting cutting surface rough cutting surface surface 6022-T4 (BLADE SHARPNESS = 0.010 in.)  5% Clearance Almost no hairlike sliver almost no hairlike slivers, No slivers, minimal burr, No slivers, minimal burr, and may large piece slivers some large pieces slivers and good cutting surface good cutting surface and particles, high burr, minimal burr, fail cutting surface rough cutting surface 10% Clearance No hairlike slivers, some No hairlike slivers, a few No slivers, minimal burr, No slivers, minimal burr, large pieces slivers and large piece slivers; high burr good cutting surface good cutting surface and particles; very high unacceptably rough cutting burr, rough cutting surface surface 15% Clearance No hairlike slivers, a few No slivers, high burr, No slivers, high burr, No slivers, high burr large piece slivers; very high unacceptably rough cutting surface rough cutting surface rough cutting surface high burr, rough cutting surface 20% Clearance No slivers, extremely high burr, No slivers, very high burr, No slivers, high burr, No slivers; high burr, very rough cutting surface unacceptable rough cutting unacceptably rough cutting unacceptable rough cutting surface surface surface 25% Clearance No slivers, extremely high burr, No slivers; extremely high No slivers; extremely high No slivers, very high burr, very rough cutting surface burr, unacceptably rough burr, unacceptably unaccetably rough cutting cutting surface rough cutting surface surface

[0049] TABLE 7 0 Degree 10 Degree 20 Degree 25 Degree 6111-T4 (BLADE SHARPNESS = 0.020 in.)  5% Clearance No hairlike sliver, many No hairlike slivers, No slivers, minimal burr, No slivers, minimal burr, large piece slivers and a few large piece slivers good cutting surface good cutting surface particles; extremely high and particles; minimal burr, burr, unacceptable cutting surface good cutting surface 10% Clearance No hairlike sliver, many No hairlike slivers; a No slivers, minimal burr, No slivers, minimal burr, large piece slivers and few large piece slivers; good cutting surface good cutting surface particles; extremely high discontinously high burr, burr, unacceptable cutting discontinously rough surface cutting surface 15% Clearance No hairlike sliver, some No sliver, extremely high No slivers; minimal burr, No slivers; minimal burr, large pieces slivers and burr, unacceptably rough fair cutting surface good cutting surface particles; extremely high cutting surface burr, unacceptable cutting surface 20% Clearance No slivers and particles; No slivers, extremely high No slivers; discontinously No slivers; discontinously extremely high burr, burr, unacceptably rough high burr, discontinously high burr, discontinously unacceptable cutting surface cutting surface rough cutting surface rough cutting surface 25% Clearance No slivers and particles; No slivers, extremely high No slivers, extremely high No slivers, discontinously extremely high burr, burr, unacceptably rough burr, unacceptably rough high burr, discontinously unacceptable cutting surface cutting surface cutting surface rough cutting surface 6022-T4 (BLADE SHARPNESS = 0.020 in.)  5% Clearance No hairlike sliver, many No hairlike slivers, No slivers, minimal burr, No slivers, minimal burr, large piece slivers and a few large piece slivers good cutting surface good cutting surface particles; extremely high and particles, burr, unacceptable cutting surface discontinously high burr and rough cutting surface 10% Clearance No hairlike sliver, many No hairlike slivers; a No slivers, minimal burr, No slivers, minimal burr, large piece slivers and few large piece slivers; good cutting surface good cutting surface particles; extremely high discontinously high burr, burr, unacceptable cutting discontinously rough surface cutting surface 15% Clearance No hairlike sliver, some No sliver, extremely high No slivers; minimal burr, No slivers; minimal burr, large pieces slivers and burr, unacceptably rough fair cutting surface good cutting surface particles; extremely high cutting surface burr, unacceptable cutting surface 20% Clearance No slivers and particles; No slivers, extremely high No slivers; discontinously No slivers; discontinously extremely high burr, burr, unacceptably rough high burr, discontinously high burr, discontinously unacceptable cutting surface cutting surface rough cutting surface rough cutting surface 25% Clearance No slivers and particles; No slivers, extremely high No slivers, extremely high No slivers, discontinously extremely high burr, burr, unacceptably rough burr, unacceptably rough high burr, discontinously unacceptable cutting surface cutting surface cutting surface rough cutting surface

[0050] TABLE 8 MAXIMUM CLEARANCE AND BLADE SHARPNESS OF CUTTING DQIF STEEL SHEET Trimming Angle Maximum Clearance Maximum Blade Edge Radius Remarks 0 Degree 13.80% 0.002 in. Extremely high and sharp burr, unacceptable cutting surface 0 Degree 13.80% 0.005 in. Extremely high and sharp burr, unacceptable cutting surface, significant local bending distortion on sheet near the cutting edge 0 Degree 17.20% 0.001 in. Extremely high and sharp burr, unacceptable cutting surface, significant local bending distortion on sheet near the cutting edge 0 Degree 17.20% 0.010 in. Not be able to cut otl the sheet metal 10 Degree  13.80% 0.005 in Not be able to cut ofi the sheet metal

[0051] The effects for each individual variable of cutting angle A, clearance C and tool sharpness R are schematically shown in FIGS. 8 to 10, respectively.

[0052] The cutting angle required for aluminum sheet differs dramatically from that for steel sheet. The best condition designed for steel results in the largest amount of slivers for aluminum, as shown in FIG. 9. As observed in the present examples, as well as in production trimming lines, slivers are not a problem for steels. A 0° trim gives the best condition to cut off the steel sheets and produces good cut surface quality and the least amount of burr. Therefore, trimming tools conventionally designed for steel sheets require cutting angles as close as possible to 0°. However, the experimental investigation conducted here showed that the 0° cutting generates the largest amount of slivers for both 6111-T4 and 6022-T4. On the contrary, with cutting angles above 15 degrees, slivers were significantly reduced or completely eliminated even with blade radii as dull as 0.020 in. for a wide range of clearances. However, as shown in FIG. 9, as the cutting angle increases and when it reaches a certain value, the burr becomes intolerable and the quality of cut surface is unacceptable even though no slivers are generated.

[0053] For steel it is usually desirable to keep clearances at about 7.5% of metal thickness. Above this value, the burr height and cut surface quality become unacceptable and it may even be impossible to cut off the sheet metal, as shown in Table 8. For 6111-T4 and 6022-T4 sheets, with appropriate cutting angles, the clearance can be 15% of the sheet thickness and result in tolerable burr height and acceptable cut surface quality. Consequently, the clearance for aluminum is less restrictive than that for steels as shown in FIG. 10.

[0054] Maintaining sharp tools is critical to trim steel sheets. As exhibited in Table 8, when the radius of the cutting blade exceeds 0.005 in. and the clearance exceeds 10%, high and sharp burrs and unacceptable cut surface quality result. However, with appropriate cutting angles for both 6111-T4 and 6022-T4 the blade edge radius can be as dull as 0.020 in. and still produce little or no slivers, low burrs and good cut surface quality, as shown in FIG. 11.

[0055] In accordance with the present invention, with appropriate cutting angles, the trimming/blanking of 6111-T4 and 6022-T4 aluminum sheets can be more robust that the trimming/blanking of steel sheets. For the aluminum alloys, the clearances can be less restrictive and tools may require less sharpening because the cutting is less sensitive to the tool sharpness. In addition, a wide range of cutting angles is possible for 6111-T4 and 6022-T4 sheets.

[0056] In accordance with the present invention, improved tool design is provided based on the results shown in Tables 1-7. Tool design guidelines for trimming 6111-T4 and 6022-T4 are shown in Table 9. The guidelines specify the clearance and maximum blade edge radius for different ranges of cutting angles. The lower bounds of the clearances are limited by sliver generation. The upper bounds of the clearances are limited by the tolerable burr height. In general, burr height increases as clearance increases and as blade sharpness decreases. Sharper blade results in lower burrs. Blade sharpness also affects the appearance of slivers. Fine hairlike slivers are generated by sharp blades. When the blade gets dull, it generates large metal pieces and particle-like slivers. TABLE 9 TRIMMING TOOL GUIDELINES FOR 6111-T4 AND 6022-T4 Trimming Angle Clearance Per Side Maximum Blade Edge Radius 0 Degree 15%-20% 0.003 in. 0-5 Degree 12.5%-17.5% 0.004 in.  5-10 Degree   10%-17.5% 0.005 in. 10-15 Degree  7.5%-17.5% 0.005 in. 15-25 Degree  5%-20% 0.010 in.

[0057] Overall, to get the best results to eliminate slivers and minimize burr height, it is preferred that the lower bounds of clearances be followed. As cutting angle increases, the clearance window opens up and the requirement for blade sharpness becomes less restrictive as shown in Table 9. Cutting angles A of 20±5 degree are the most preferred cutting conditions for trimming 6111-T4 and 6022-T4. Under such conditions, no slivers were generated in the examples and the burr heights were minimal using blades with edge radii up to 0.020 in.

[0058] A cutting angle A of zero degrees is possible if the clearance is increased from 7.5±2.5% (designed for steel) to 15% to 20% of the aluminum sheet thickness. Since burr height increases with blade edge radius, the cutting blade needs to be maintained as sharp as possible to reduce the burr height.

[0059] For a quantitative indication of burr severity, the burr heights were measured for 0 degree cutting for different clearances with different blade sharpnesses. The burr heights were measured using micrographs of the cross-sections of trimmed samples. The burr heights are given in Table. 10. TABLE 10 0.001 in. 0.002 in. 0.005 in. 0.010 in. 0.020 In. Burr Height of 6111-T4  5% Clearance 0.05 mm 0.055 mm  0.05 mm  0.06 mm  0.35 mm 10% Clearance 0.10 mm 0.120 mm 0.140 mm 0.183 mm  0.35 mm 15% Clearance 0.133 mm  0.133 mm 0.183 mm 0.233 mm  0.35 mm 20% Clearance 0.15 mm  0.20 mm 0.183 mm 0.233 mm  0.40 mm 25% Clearance 0.167 mm  0.183 mm 0.233 mm 0.317 mm  0.40 mm Burr Height of 6022-T4  5% Clearance 0.058 mm  0.117 mm 0.133 mm 0.167 mm 0.317 mm 10% Clearance 0.133 mm  0.117 mm 0.142 mm 0.183 mm 0.333 mm 15% Clearance 0.10 mm 0.158 mm 0.183 mm 0.225 mm 0.35 mm 20% Clearance 0.20 mm 0.15 mm  0.167 mm 0.292 mm 0.367 mm 25% Clearance 0.15 mm 0.10 mm  0.225 mm 0.292 mm 0.367 mm

[0060] In accordance with the present invention, the selection of the appropriate cutting angle A results in improved trimming of aluminum sheet in comparison with steel sheet. In addition, the clearance C used in trimming aluminum sheet can be varied within a relatively wide range in comparison with the relatively small clearance required for trimming of steel sheet. Furthermore, the tools used for trimming require less sharpening and allow the use of a relatively dull cutting blades by adjusting the cutting angle and clearance used to trim the aluminum sheet. These advantages result in a robust trimming operation in comparison with conventional steel trimming methods.

[0061] Whereas particular embodiments of the present invention have been described herein, it is to be understood that various changes, additions, adaptations and modifications may be made without departing from the scope of the invention, as set forth in the appended claims. 

What is claimed is:
 1. A method of trimming aluminum sheet comprising cutting the aluminum sheet at a cutting angle and with a cutting blade clearance which substantially eliminate the formation of aluminum slivers.
 2. The method of claim 1, wherein the cutting angle is from about 15 to about 25 degrees and the clearance is from about 5 to about 20 percent of the thickness of the aluminum sheet.
 3. The method of claim 2, wherein the cutting blade has a maximum edge radius of up to about 0.25 mm.
 4. The method of claim 1, wherein the cutting angle is from about 10 to about 15 degrees and the clearance is from about 7.5 to about 17.5 percent of the thickness of the aluminum sheet.
 5. The method of claim 4, wherein the cutting blade has a maximum edge radius of up to about 0.125 mm.
 6. The method of claim 1, wherein the cutting angle is from about 5 to about 10 degrees and the clearance is from about 10 to about 17.5 percent of the thickness of the aluminum sheet.
 7. The method of claim 6, wherein the cutting blade has a maximum edge radius of up to about 0.125 mm.
 8. The method of claim 1, wherein the cutting angle is from 0 to about 5 degrees and the clearance is from about 12.5 to about 17.5 percent of the thickness of the aluminum sheet.
 9. The method of claim 8, wherein the cutting blade has a maximum edge radius of up to about 0.1 mm.
 10. A method of trimming aluminum sheet comprising: securing an aluminum sheet at a cutting angle of at least about 10 degrees adjacent a cutting blade; trimming the aluminum sheet at the cutting angle with the cutting blade; and recovering the trimmed aluminum sheet with substantially no slivers.
 11. The method of claim 10, further comprising securing the aluminum sheet between a die and a pad.
 12. The method of claim 11, further comprising securing the aluminum sheet at a cutting angle of from about 15 to about 25 degrees.
 13. The method of claim 12, further comprising providing a clearance between the cutting blade and the die of at least about 10 percent of the thickness of the aluminum sheet.
 14. The method of claim 13, wherein the clearance is less than about 20 percent of the thickness of the aluminum sheet.
 15. The method of claim 13, wherein the clearance is from about 10 to about 17.5 percent of the thickness of the aluminum sheet.
 16. The method of claim 15, further comprising providing the cutting blade with an edge radius of up to about 0.25 mm.
 17. The method of claim 10, further comprising providing the cutting blade with an edge radius of up to about 0.75 mm.
 18. The method of claim 10, wherein the aluminum sheet comprises an alloy selected from the group consisting of Aluminum Association alloys 6111 and
 6022. 19. The method of claim 18, wherein the aluminum sheet comprises aluminum alloy 6111-T4.
 20. The method of claim 18, wherein the aluminum sheet comprises aluminum alloy 6022-T4.
 21. The method of claim 10, wherein the aluminum sheet comprises an autobody sheet.
 22. A method of trimming aluminum sheet comprising: securing the aluminum sheet between a die and a pad; trimming the aluminum sheet with a cutting blade having a clearance between the cutting blade and the die of at least about 15 percent of the thickness of the aluminum sheet; and recovering the trimmed aluminum sheet with substantially no slivers.
 23. The method of claim 22, wherein the clearance is from about 15 to about 20 percent of the thickness of the aluminum sheet.
 24. The method of claim 23, further comprising providing the cutting blade with a tool sharpness of up to about 0.075 mm.
 25. An apparatus for reducing sliver production during trimming of aluminum sheet comprising: means for cutting the aluminum sheet; and means for securing the aluminum sheet adjacent the cutting means at a cutting angle of at least about 10 degrees.
 26. The apparatus of claim 25, wherein the means for securing the aluminum sheet comprises a die and pad for holding the aluminum sheet therebetween.
 27. The apparatus of claim 26, wherein the die and pad secure the aluminum sheet at a cutting angle of from about 15 to about 25 degrees.
 28. The apparatus of claim 27, further comprising a clearance between the cutting blade and the die of at least about 10 percent of the thickness of the aluminum sheet.
 29. The apparatus of claim 28, wherein the clearance is less than about 20 percent of the thickness of the aluminum sheet.
 30. The apparatus of claim 28, wherein the clearance is from about 10 to about 17.5 percent of the thickness of the aluminum sheet.
 31. The apparatus of claim 30, wherein the cutting blade has an edge radius of up to about 0.25 mm.
 32. The apparatus of claim 25, wherein the cutting blade has an edge radius of up to about 0.75 mm.
 33. The apparatus of claim 25, wherein the aluminum sheet comprises an alloy selected from the group consisting of Aluminum Association alloys 6111 and
 6022. 34. The apparatus of claim 33, wherein the aluminum sheet comprises aluminum alloy 6111-T4.
 35. The apparatus of claim 33, wherein the aluminum sheet comprises aluminum alloy 6022-T4.
 36. The apparatus of claim 25, wherein the aluminum sheet comprises an autobody sheet.
 37. A trimmed aluminum sheet substantially free of slivers produced by securing an aluminum sheet at a cutting angle of at least about 10 degrees adjacent a cutting blade, and trimming the aluminum sheet at the cutting angle with the cutting blade.
 38. The trimmed aluminum sheet of claim 37, wherein the cutting angle is from about 15 to about 25 degrees.
 39. The trimmed aluminum sheet of claim 38, wherein the aluminum sheet is secured with a cutting blade clearance of at least about 10 percent of the thickness of the aluminum sheet.
 40. The trimmed aluminum sheet of claim 39, wherein the clearance is less than about 20 percent of the thickness of the aluminum sheet.
 41. The trimmed aluminum sheet of claim 40, wherein the cutting blade has an edge radius of up to about 0.25 mm.
 42. The trimmed aluminum sheet of claim 37, wherein the aluminum sheet comprises an alloy selected from the group consisting of Aluminum Association alloys 6111 and
 6022. 43. The trimmed aluminum sheet of claim 42, wherein the aluminum sheet comprises aluminum alloy 6111-T4.
 44. The trimmed aluminum sheet of claim 42, wherein the aluminum sheet comprises aluminum alloy 6022-T4.
 45. The trimmed aluminum sheet of claim 37, wherein the aluminum sheet comprises an autobody sheet. 